Apparatus and method of fractionation of ethyl benzene



A. K. REDCAY Aug. 9, 1966 Original Filed Oct. 23, 1959 E n w 1|lI WILL/ 1 l||| D w United States Patent O 3,265,590 APPARATUS AND METHOD F FRACTIONATION 0F ETHYL BENZENE Aaron K. Redcay, Florham Park, NJ., assignor to The Badger Co., Inc., a corporation of Massachusetts Continuation of applications Ser. No. 848,389, Oct. 23,

1959, and Ser. No. 127,469, July 28, 1961. This application .lune 23, 1964, Sel'. No. 379,432

13 Claims. (Cl. 203`21) The present application is a continuation of United States application Serial No. 848,389, filed October 23, 1959 and entitled Ethyl Benzene Fractionation and Steam Generation System and application Serial No. 127,469 filed Iuly 28, 1961.

The present invention relates to a process for the separation of mixtures of ethyl benzene Iand meta, ortho and para xylenes, specifically a pro-cess for the separation of ethyl benzene of purity sufficient to manufacture polymer grade styrene and at the same time produce sufficient steam to make the process economical.

Until very recently the only method of manufacture of styrene grade ethyl benzene was -to start with ethylene and benzene of suitable purity. The benzene had to be of a purity of the order of 99% while'the ethylene purity was not extremely critical; provided that the impurities consisted of light parains inerts and/ or hydrogen.

In spite of the fact that the mixed petroleum xylenes (which contain substantial percentages of ethyl benzene)` are a readily .available source of ethyl benzene, separation thereof had not been seriously attempted in view of the extremely close boiling points of the components of the mixture as well as their great similarity in chemicalstructure.

More recently a process for the distillation of lethyl benzene from the mixed petroleum xylenes has been proposed but this process operates atv atmospheric pressure and possesses certain economic disadvantages. More spe; cifically this process has been operated commercially in areas where fuel costs are low. However, the success of this operation is markedly improved if the operation is conducted in the manner described' by this invention. Moreover, in areas where fuel `costs arehgh, operation in the manner described by this invention may be the difference between success and failure.

Therefore, it is among the objects of this invention to provide a process for the manufacture of styrene grade` purity ethyl benzene without the necessity of the use of pure starting material. V I 1 Another object of the present invention is to provide apparatus for fractionating ethyl benzene yand the' xylene isomers at elevated pressure, making it possible to reduce the physical size of the apparatus for a given through-put and making it possible to utilize waste hea-t from the fractionation for the generation of steam. It is also among the objects of this invention to provide a process for the production of styrene grade ethyl ben` zene from readily available petroleum xylenes. v

It is further Aamong the objects of this invention to provide a process for effecting the separation .of mixtures of ethyl benzene and meta, ortho and paraxylenes in an economical manner. 'l l Y It is still further among the objects of this invention to provide a process for the separation of petroleum xylenesethyl benzene mixture whereinuseful steam is generated:

It is still further among the objects of this invention to provide a process for the separation of mixed petroleum xylenes containing ethyl benzene wherein smaller and less expensive equipment may be used.

In practicing the present invention the readily available mixtures of ethyl benzene Iand ortho, 'meta and paraxylenes are distilled in a column under at least 2 p.s.i.g.

x 3,265,590 Patented August 9, 1966 ICC The distillation is carried out in a multi-stage column and the reuxing ratio is from 40 to 200:1.

The mixture is separated into an overhead fraction and bottom fraction, the former containing styrene grade ethyl benzene (usually in excess of 99% and the bottom fraction containing the remaining mixed xylenes. The overhead fraction is passed through a steam generating heat exchanger whereby useful quantities of steam at a pressure of `at least 20 p.s.i.g. are produced. The ethyl benzene is entirely satisfactory for use in the manufacture of styrene, which in turn is used for yvarious synthetic rubber formulations and the like. t

The column should contain from 150 to 500 distillation stages and the column distillation pressure should be not over 150 p.s.i.g. By variation in distillation pressure, it has been found possible to generate steam at pressures up to .about 785 p.s.i.g. In the appended drawing there is shown a schematic flow sheet representing the apparatus and system of the. present invention.

As shown in the drawing, the feed stock-which may consist of the usual mixture of ethylbenzene, orthoxylene, meta-xylene and para-xylene and closely relatedv hydrocarbons which results from a conventional isomeri-I zation procedure-is introduced into a feed accumulator 10 provided with a constant-level control 12 for inlet valve 14. From accumulator 10 the feed is pumped by means of centrifugal pump 16 through a constant-flow control valve 18 and through one side ofeach of heat exchangers 20, 22, whence it passes into fractionator column 24. Fractionator column 24 may be a conventional multiplate -column adapted for operation at elevated pressures of the order of 23 to 150 p.s.i.g. As the feed stock enters column 24, its temperature will have been raised close to the boiling point by means of the heat exchangers 20, 22, the heat supplies for which will be described below. The necessary heat for vaporizing the feed stock is supplied by recirculating the liquid at the bottom of the tower through centrifugal pump 26'and heater 28. A differential pressure control 30 actuated` by. the dierential pressure between spaced plates of column 24, i.e. between points in the Column approximately l0 to l5 plates apart, is provided for controlling valve 32 which controls the input of fuel to heater 28. The portion of the bottoms which does not pass through heater 28 is,

*l passed through the second side of heat exchanger 22 in l into a reux and product accumulator 38 from which the liquid overhead fraction is pumped by means of pump 40. A `por-tion of the pump output passes through a constant-y flow regulator 42 back to the top of column'24 in reflux; while the remaining portion ofthe output of pump 40 passes through valve 44 and through the second side of heat exchanger 20, serving to heat the feed stock, and finally through .a water-cooled cooler 46 to storage.l The volume or quantity of the overhead fraction passed to storage is controlledby valve 44 which in turn is controlled by a constant-level control device 48` mounted on accumulator 38. v v

The water feed for heat exchanger 36 which serves ,as the steam generator is introduced through a steam-water separator 50, the rate of introduction being controlled by valve 52 which in turn is controlled by a constant-level control device 54 mounted on the separator 50. Pump 56 pumps the water from separator 50 through valve 58 to heat exchanger 36, valve 58 being controlled by pressure regulator 60 responsive to the vapor pressure in reux and product accumulator 38 which in turn ofcourse is directly related 'to the pressure in column 24. Steam generated in heat exchanger 36 is returned to separator 50, whence it is withdrawn for use.

The differential presure control of the fuel input for heater 28, together with the constant-flow control 18 on the stock input or'feed, serves to maintain the operation of fractionator column 24 in a steady state within predetermined limits. Control of the water feed to heat exchanger 36 by means of valve 58 provides control of the absolute pressure within column 24. Inasmuch as operation of valve 58 is responsive to the vapor pressure Within product accumulator 38 which in turn is equal to the pressure of the overhead fraction within column 24 except for whatever pressure drop occurs lthrough heat exchanger 36, the absolute pressure Within column 24 is maintained constant within predetermined limits. By maintaining the pressure within column 24 between 23 and 150 p.s.i.g., it is found that the temperature of the overhead entering heat exchanger 36 is from 306 to 475 F. This permits generation of steam within heat exchanger 36 at a temperature of 259 to 450 F. and at a pressure of 20 to 405 p.s.i.g., or preferably at 281 to 450 F. and 35 to 405 p.s.z'.g., which is within the range of usual industrial steam supplies.

It will be apparent from the foregoing that operation of the above-described fractionating system not only will effectively separate ethyl benzene from closely boiling xylenes and other hydrocarbon products but also will utilize waste heat from the fractionating operation to provide a supply of steam at industrially useful temperatures and pressures. Operation of fractionating column 24 at elevated pressure also makes it possible to reduce the physical size of the column required for a given through-put, thus reducing the cost of the installation. The system obviously may include two or more fractionator columns operated in tandem or even in sequence, if desired, and controlled in thesame manner as described above for one column.

To more specifically illustrate the nature of the present invention, reference is made to the following examples:

Example 1 A mixture of petroleum xylenes and ethyl benzene is distilled under 29 p.s.i.g. pressure (365 F.) in a multistage reflux column having 199 distillation stages. The reflux ratio is 72 to 1 and the overhead product produced is ethyl benzene of 99.8% purity. This product is 'suitable for the manufacture of styrene. The overhead product generates steam at 90 p.s.i.g. on passage through a suitable steam generator.

Example 2 A mixture of petroleum xylenes, ethyl benzene and toluene is distilled under 40 p.s.i.g. pressure (376 F.) in a multi-stage reux column having 218 distillation stages. The reflux ratio is 77 to 1 and the overhead product is 92.06% pure ethyl benzene. This product on being cooled in a steam generator, generated steam at 150 p.s.i.g. and is suitable for the manufacture of styrene.

Example 3 A mixture of petroleum xylenes and ethyl benzene is distilled in a multi-stage reflux columnunder 29 p.s.i.g. (368 F.) The column is provided with 179 distillation stages and the reflux ratio is 38 to 1. The overhead product is 99.8% pure ethyl benzene suitable for styrene manufacture. At the same time the overhead product generates steam at 90 p.s.i.g. v

Example 4 A mixture of petroleum xylenes and ethyl benzene is distilled in a multi-stage reflux column having 251 distillation stages under 29 p.s.i.g. pressure. The reflux ratio is 343 to 1 and the overhead product is 99.8% pure ethyl benzene. This product, suitable for styrene manufacture, generates steam at 90 p.s.i.g.

,.4 Example 5 A mixture of petroleum xylenes and ethyl benzene is distilled in a multi-stage reflux column having 157 distillation stages under 2 p.s.i.g. pressure (286 F.). The reflux ratio is 58 to 1 and the overhead product is 99.8% pure ethyl benzene. The overhead product generates steam at 20 p.s.i.g. and is suitable for styrene manufacture.

Example 6 A mixture of petroleum xylenes and ethyl benzene is distilled in a multi-stage reflux column under p.s.i.g. pressure (494 F.). The column is provided with 239 distillation stages and the reflux ratio is 104 to l. The overhead product is 99.8% pure ethyl benzene suitable for styrene manufacture. At the same time, the overhead product generated steam at 785 p.s.i.g.

Example 7 Minimum Maximum Tower Distillation Pressure, p.s.i.g 3 65 Reflux Ratio 60 to 1 120 to 1 Distillation Stages 180 400 Steam Generation Pressure, p. .g 50 150 While .only six speci-lic exampl of the present invention have been set forth, nevertheless such changes as will be apparent to -one having reasonable skill in the art may be made Without departing from the spirit thereof. For example, the feed may be preheated by the overhead (after it has left the steam generator) and/or by the bottoms and additional Iheat exchangers may be provided to further cool either the overhead or the bottoms if necessary or desirable. Thus it can be seen that the present invention is to be broadly construed and not to be limited except by the character of the claims appended hereto.

What is claimed is:

51. A method of separating a mixture of ethyl benzene and ortho, meta and para xylenes comprising dist-illing saidv mixture under at least 2 p.s.i.\g. pressure and a temperature of at least 286' F. in a multi-stage column, reuxing said mixture lat a ratio of from 38 to 350: 1, whereby said mixture separates into an overhead fraction of styrene grade ethyl :benzene and .a bottom fraction, passing said overhead fraction `from said column through a heat exchanger, yand generating steam at a pressure of at least 20 p.s.i.g. Y

2. A method according to claim 1 wherein said overhead fraction consists of styrene grade ethyl benzene.

3. A method according to claim 1 wherein said column contains from 150 to 500 theoretical plates.

4. A method according to claim 1 wherein the pressure in said column is not over 150 p.s.i.g.

S. A method according to claim 1 4wherein the pressure of said steam is not over 785 p.s.i.g.

6. Apparatus for the separation of a mixture comprising ethyl benzene, ortho-xylene, meta-xylene and paraxylene and for the production of steam comprising means for providing a feed of said mixture, a first heat exchanger having rst and second sides, a second heat exchanger having first and second sides, a fractionating column, means ifor passing said ffeed through the `first sides of both said heat exchangers and into said column. means for supplying heat to said column to vaporize at least a portion of said feed, a third heat exchanger having rst and second sides, means for passing the vaporized overhead fraction from said column through the rst side of said third heat exchanger to condense said fraction, means for .passing a `first portion of said condensed overhead fraction through the second side of said rst heat exchanger, means for passing a second portion of said condensed loverhead fraction rback to 'said Kcolumn Iin reux means .for passing the liquid bottom fraction from said column through the -second side of said second heat exchanger, means for passing water through the second side of said third heat exchanger to generate steam, and means responsive to the differential pressure between spaced plates within said column for controlling the quantity of heat supplied to said column and pressure-responsive means for controlling the quantity of water supplied to said third heat exchanger to maintain the operating pressure within said column above 23 p.s.i.g. and to generate said steam at a pressure of at least 20 p.s.i.g.

7. Apparatus as dened in claim 6 in which said pressure-responsive means includes in addition means responsive to the vapor pressure of said overhead fraction for controlling the water input to said third heat exchanger.

8. Apparatus for separating ethyl benzene from admixture with xylenes which consists in a substantially vertical fractionating column, a heater having a connection from thebottom of said column `for ow of liquid, an exit from said heater for said liquid Iinto the lower part of said column, said heater adapted to heat said liquid to a temperature of about 306-47 5 F., means for maintaining a pressure of about 23150 p.s.i. in said column, .a diierential pressure control at the central part of said column connected `to said heater to control the supply of fuel thereto, a irst heat exchanger connected to the central part of said column and through which said Iadmixture is adapted to flow into said column, a second heat exchanger and a connection from the upper part of said column thereto for flow of vapors to be codensed therein, a steam generator in said second heat exchanger with means for maintaining super-atmospheric pressure in said steam generator, an accumulator connected to said second heat exchanger for holding said condensed vapors.

9. Apparat-us according to claim 8 in which there is a connection for ilow of condensed vapors from said accumulator through said first heat exchanger in heat exchange relation to said admixture.

10. Apparatus according to claim v8 in which there is a connection from the bottom of said column for ow of liquid through a third heat exchanger in heat exchange relation to said admixture.

11. A method of separating ethyl benzene from admixture with xy=lenes which consists in preheating said mixture, introducin-g said mixture into the central portion of a fractionating column; maintaining a pressure of about 23-150 p.s.i. in said column, heating said column by circulating .a portion of said mixture through a heater to produce a temperature of about 306475 F. in the vapors exiting from the top of said column; controlling said temperature by the difference in Ipressure between lvertically spaced points in said column; passing said vapors into heat exchange relation with water at a temperature of about 259-450 F. thereby forming a mixture of steam and water, said vapors being condensed; returning a portion of said condensate to the upper part of said column, and recovering the remainder -as ethyl benzene; and separating the steam from the water at superatmospheric pressure.

12. A method Iaccording to claim 11 wherein the pressure in said column is not over i p.s.i.g.

13. A method according to claim 11 wherein the pressure of said steam is not over 405 p.s.i.g.

References Cited by the Examiner UNITED STATES PATENTS 2,489,949 11/11949 Blair 202-160 2,509,136 5/1950 Cornell 202,-160 X `2,696,465 12/ 1955 Kittredge. 2,726,275 12/1955 Lien et al. 260-674 X 2,959,626 111/1960 Krausse et al. 202--39.5

NORMAN YUDKOFF, Primary Examiner.

F. E. DRU-MMOND, Assistant Examiner. 

1. A METHOD OF SEPARATING A MIXTURE OF ETHYL BENZENE AND ORTHO, META AND PARA XYLENES COMPRISING DISTILLING SAID MIXTURE UNDER AT LEAST 2 P.S.I.G. PRESSURE AND A TEMPERATURE OF AT LEAST 286* F. IN A MULTI-STAGE COLUMN, REFLUXING SAID MIXTURE AT A RATIO OF FROM 38 TO 350:1, WHEREBY SAID MIXTURE SEPARATES INTO AN OVERHEAD FRACTION OF STYRENE GRADE ETHYL BENZENE AND A BOTTOM FRACTION, PASSING SAID OVERHEAD FRACTION FROM SAID COLUMN THROUGH A HEAT EXCHANGER, AND GENERATING STEAM AT A PRESSURE OF AT LEAST
 20. P.S.I.G. 